This invention relates to a vision unit which is easily assembled into the opening of a door. More particularly, this invention relates to a frame structure for a vision panel approved for use in a fire door wherein the frame structure can be easily assembled yet will secure the approved wire glass even if sprayed with a fire hose after 11/2 hours in a 1700.degree. F. fire.
There are currently available vision panel frames for doors which use frame members having opposing wide flat steel surfaces to secure the glass. The frame members are joined by through bolts or screws. The screws apply clamping pressure to the glass and the door faces. Since the contact area between the frame and the glass is quite large, the clamping pressure per square inch is very low. The design of this invention reduces the contact area between glass and frame to a single edge. The frame of this invention also positions the thru bolts very close to the glass, increasing the percentage of clamping pressure applied to the glass. These two features dramatically increase the clamping force per square inch applied to the glass. Since this clamping force is high per square inch, the frame described herein will embed its clamping edge into the semi-molten glass of a 1700.degree. F. fire, holding the glass securely, whereas currently available vision panel frames having considerably less clamping force per square inch on the glass, will allow the semi-molten, sagging glass to slip out of the frame in a hot fire.
Another disadvantage of currently available vision panel frames is that they must be of one piece welded construction to pass required fire tests. Currently available frames are very fragile until installed and shipping is a major problem. The bulk of the shipping carton, along with the fragile contents, results in significant shipping damage. In a preferred manner, each unit of the frame of this invention can be manufactured as eight individual linear sections to form the sides of the frame. These sections can be packaged in a strong, tubular package and easily shipped without damage. The eight pieces can be easily assembled at the job site just prior to installation in the fire door. Another disadvantage of currently available vision panel frames is that the door must be drilled to provide the holes for the screws. This installation operation is expensive as the door must be drilled from both sides to prevent splintering of the door skin. The vision panel frame herein disclosed allows the screws to pass thru the door cutout, eliminating the need to drill screw holes. There is also available a window unit as described in U.S. Pat. No. 3,969,857 wherein the fastening screws pass inside the door cutout and engage a flange which engages the glass on the opposite side. In this particular design, the glass can be very easily broken if the screw tension is not drawn up properly. While this design does allow one face of the frame to be without screw holes, it does not result in the two sides being not symmetrical and two different cross sections must be manufactured to make one complete frame. This results in expansion of inventory. Further, this particular frame structure is not easily assembled by a person acting alone.
It is an advantage of the present invention to provide a vision unit which is easily assembled yet can withstand the high rigors of heat and other adverse conditions. It is still another advantage to provide a frame unit for a vision panel which can be easily installed by a person acting alone from a ready to assemble kit. Other advantages are a simplified frame structure for a fire door, which is composed of a minimum number of parts thereby reducing inventory costs while at the same time offering versatility in design.